Process of protecting surfaces of metals against corrosion



United States Pater PROCESS OF PROTECTING SURFACES OF METALS AGAINSTCORROSION Josef M. Michel and Karl F. Hager, Huntsville, Ala., assignorsto the United States of America as represented by the Secretary of theArmy No Drawing. Application July 16, 1951, Serial No. 237,051

Claims. (Cl. 117-127) (Granted under Title 35, U. S. Code (1952), see.266) The invention described herein may be manufactured and used by orfor the Government for govermental purposes without the payment of anyroyalty thereof.

Different ways are known to protect metals and alloys against corrosion,e. g., oxide and phosphate coatings, paints, varnishes, plating, etc.The protection obtained by this means may be called permanent.

However, there are other conditions where corrosion, especially rustprevention has to be temporary only, like metal parts in storage orbetween processing steps. In this case, valuable agents are petroleumderivatives, suitably chosen fractions, which usually meet therequirements of the industries in question and may be able to give anadequate protection. However, it was found that they cannot providecompletely satisfactory results when conditions encountered in practicaluse are too severe.

Therefore, it was important to search for compounds that, likeinhibitors, prevent corrosion even when added in small amounts only topetroleum derivatives. It stands to reason that such additives must notchange the favor able qualities of the base material like easyapplication, no cracking, peeling or slipping, no hardening, easyremoval, lubricating properties, etc. The best way to reach this goal isto have a compound that is completely soluble in the agents in question.

It was found that the hydrocarbon-sulfamido-carboxylic acids as well astheir inorganic and organic salts are highly effective corrosionpreventives, even when added in small quantities to hydrocarbons ormixtures of such compounds with solvents, e. g., alcohols, ethers,ketones, aldehydes, mobile hydrocarbons and chlorinated hydrocarbons andother liquid non-aqueous solvents in which electrolytic dissociationdoes not occur. These solvents may be added to the petroleum derivativesin order to obtain solutions that can be handled easily, e. g., bydipping or spraying the metal parts even at low temperatures. Ethanol,benzene and acetone may be used as such solvents. Such solvents also actas thinning agents for the hydrocarbon oil.

In those instances where a film or coating of a lubricating oil upon thetreated metal surface is unnecessary or undesired, thehydrocarbon-sulfamido-carboxylic acids may be dissolved in the solventsmentioned without the inclusion of any additional vehicle of the natureof petroleum derivatives or hydrocarbon lubricants. It is pointed outthat in the practice of the invention thehydrocarbon-sulfamido-carboxylic acids, or the salts thereof, usedaccording to the present invention are in real or true solution in thepetroleum derivatives or hydrocarbon oils, and in the solvents referredto above, and in the mixtures of such solvents with the petroleumderivatives or lubricating oil. The practice of the invention results inthe formation of a film or coating of these real or true solutions uponthe surface of the metal to be protected against corrosion.

The said hydrocarbon-sulfamido-carboxylic acids can be designated by thechemical formula RSO2NHR1COOH, where R is an alkyl radical of from 5 to20 carbon atoms, and R1 an alkyl radical less one hydrogen atom. inother words, R1 is a divalent saturated aliphatic radical, one valencybond of which is connected with the carbon atom of the carboxyl groupand the other valency bond of which is connected with the nitrogen atomof the RSOaNH group. Examples of hydrocarbon-sulfarmdocarboxylic acids,or the salts thereof, which may be used according to the invention are:octadecylsulfamido acetic acid (CmHzqSOzNHCHzCOOH), octylsulfamidobutyric acid (CsHnSOzNHCsHeCOOH) and others given in the examples below.The hydrocarbon-sulfamido-carboxy1ic acids that are used in the practiceof the invention may be regarded as derivatives of the lower fatty acids(CnHanOz), such as formic, acetic, propionic and butyric acids in whicha hydrogen atom attached to a carbon atom has been replaced by the groupNHSOzR, where R is a univalent saturated hydrocarbon radical of from 5to 20 carbon atoms in either a straight or branched chain, butpreferably in a straight chain.

Examples of salts of hydrocarbon-sulfamido-carboxylic acids that may beused in practicing the invention are: inorganic salts such as sodium,potassium, and ammonium salts, and salts of ammonia derivatives such ahydroxylamine and hydrazine; and organic salts such as salts ofcyclohexylamine, methylamine and ethylamine.

The hydrocarbon-sulfamido-carboxylic acids or the salts thereof, inaccordance with the present invention, may be mixed with or dissolved inthe hydrocarbon petroleum derivative, for example a hydrocarbonlubricating oil either as such or thinned or rendered more mobile by theadmixture therein of solvents as above mentioned, in proportions varyingover a wide range, for example from 0.1 percent to 50.0 percent. Thecomposition so prepared is preferably used at a pH value of 7 or less.The pH value of the composition when the salts of thehydrocarbon-sulfamido-carboxylic acids are used is regulated to the pHvalue of 7 or less by incorporating into the composition a freehydrocarbon-sulfamido-carboxylic acid, preferably the free acidcorresponding to the salt used. In those instances where the petroleumderivative or hydrocarbon oil is not mixed with the said solvents andthe solvents alone are used to dissolve the saidhydrocarbon-sulfamido-carboxylic acids, or salts thereof, the said acidsand salts are also used in proportions of from 0.1 percent to 50.0percent, with adjustment of the solutions of the salts to a pH value of7 or less by the addition of a corresponding acid or acid of the sameclass.

The compositions described herein when used in practicing the inventionare free of a separate phase of water or a separate phase of a watersolution. While petroleum derivatives, such as lubricating oils, andsolvents such as alcohols, ethers, ketones, etc. may contain a certainamount of dissolved Water, such water is not associated with them as aseparate or free phase, such as would exist for example in a dispersionor emulsion. The expression substantially free of water as used in theappended claim is intended to mean that water is not present insubstantial amounts as a separate or free phase either as water as such,or as water solutions of some solutes, but the said expression is notintended to exclude water that may be present in dissolved condition inthe petroleum derivative or solvents mentioned above or in mixtures ofthem.

Exposure, humidity and spraying tests showed excellent results insofaras even under these serious conditions, no formation of rust or othercorrosion products was observed.

It is recommended that metal parts which are dirty or partially corrodedbe cleaned by proper treatment before the procedure is applied withlasting success. On the other hand, protected equipment can either beused as it is, because of the high lubricating power of thehydrocarbon-sulfamido-carboxylic acids and their salts or they can becleaned easily, if necessary, as these compounds are also highlyeffective emulsifiers.

The following examples show the high protective power of differentmixtures containing compounds of hydrocarbon-sulfamido-carboxylic acidsand their salts:

Example #1 Iron specimens, /1 x 5 x A" have been cleaned by sandblasting and washing with benzene. The dried samples are dipped forabout 10 minutes into test tubes containing petrolatum, heavy liquid U.S. P., at ambient temperature. Test tube #1 contained nothing but thispetrolatum; test tube #2 contained an additional admixture of 1%octadecylsulfamido acetic acid sodium salt; test tube #3 contained 10%of the same inhibitor. The samples were allowed to lose their adherentsurplus oil while standing at ambient temperature. Then they weretreated in a weather chamber for a longer period of time. After 3 hourstesting using tap water, the efficiency of the added inhibitor appearedclearly; specimen #1 treated with pure petrolatum was covered all overthe surface with rust but specimens #2 and #3 stood unchangedcompletely.

Example #2 Iron specimens, same kind as in Example 1, have been dippedinto the following preservatives:

a. Lubricating oil, heavy.

b. Lubricating oil, heavy, and 0.5% octylsulfamido butyric acid ammoniumsalt.

c. Lubricating oil, heavy, and 5.0 octylsulfarnido butyric acid ammoniumsalt.

Temperatures of about 70 C. and a dipping period between 2 and 5 minuteswere used. After testing in the weather chamber the same remarkabledifference was observed: on specimen (a) first corrosion phenomenaappeared after 30 minutes while the other samples (b) and containing 0.5and 5.0% inhibitor remained unchanged even after several hours oftesting.

Example #3 Dow Metal M (containing 98.5% Mg, 1.5% Mn) specimens, A x x 1inches, wet scrubbed with pumice, rinsed with water containing 0.1%sodium bichromate, were dried and dipped in the following solutions atambient temperature for about 10 minutes:

a. 50% petrolatum, 50% benzene.

b. Same as (a) with 4% R-sulfamido acetic acid, where R=a mixture ofaliphatic hydrocarbons with a chain length between 12 and 18 carbonatoms.

After one day storage under normal conditions in the laboratory, thesamples were tested in a chamber by repeated spraying with 1% sodiumchloride solution.

The difference as to corrosion resistance is distinctly seen. Whilesamples (a) showed severe corrosion after one hour treatment, specimenstreated with inhibitor containing solution described under (b) remainedunchanged even after several hours treatment of the same kind.

Example #4 Different parts of a fuel pump (cast iron) cleaned andderusted by a cathodic treatment in a 15% NaOH solution at a temperaturebetween 50-60 C., rinsed and dried afterwards, were protected againstcorrosion by spraying with the solutions as follows:

a. Oil fraction consisting of hydrocarbons with a chain length between10 and 16 carbon atoms.

b. Same fraction as mentioned under (a) with addition of 15%dodecylsulfamido sodium propionate-5% dodecylsulfamido propionic acid.

After two days storage at ambient temperature, the

different metal parts were tested in a humidity chamber at elevatedtemperature (-80 C.) for 36 hours. While the specimens treated withsolution (a) showed severe corrosion, the other ones protected by theoil containing inhibitors named under (b) were entirely unchanged.

These examples show precisely that this special group of highly metalactive inhibitors are fully effective already after a few minutestreatment. Therefore, if they are allowed to react even for a muchlonger time during storage this protection will become better and betterwith the lapse of time.

We claim:

1. The process of protecting a metal surface against corrosion whichcomprises applying to said surface a solution comprising a majorproportion of a liquid hydrocarbon and a minor proportion of octadecylsulfamido acetic acid sodium salt.

2. The process of protecting a metal surface against corrosion whichcomprises applying to said surface a solution comprising a majorproportion of a liquid bydrocarbon and a minor proportion ofoctylsulfamido butyric acid ammonium salt.

3. The process of protecting a metal surface against corrosion whichcomprises applying to said surface a solution comprising a majorproportion of liquid hydrocarbon and a minor proportion of a mixture ofcompounds having the formula RSOzNI-ICHnCOOH in which R is an alkylchain of 12 to 18 carbon atoms.

4. The process of protecting a metal surface against corrosion whichcomprises applying to said surface a solution comprising a majorproportion of a liquid hydrocarbon and a minor proportion of a mixtureof dodecylsulfamido sodium propionate and dodecylsulfamido propionicacid.

5. The process of protecting a metal surface against corrosionwhichcomprises applying to said surface a coating of a solution,selected from the group consisting of petrolatum and lubricating oil andcontaining from 0.1 to 50.0 percent of a compound having the formulaRSO2NHR1COOR2 in which R is an alkyl radical of from 5 to 20 carbonatoms, R1 an alkyl radical in which one of the hydrogen atoms has beenreplaced by the RSOzNH-group of said compound, and R2 is selected fromthe group consisting of a hydrogen atom, an alkali metal atom, anammonium radical and an organic salt radical, said solution beingsubstantially free of water.

References Cited in the file of this patent UNITED STATES PATENTS2,225,960 Orthner et a1. Dec. 24, 1940 2,520,356 Bishop Aug. 29, 19502,578,725 Michel et a1. Dec. 18, 1951 2,602,760 Michel et al. July 8,1952

1. THE PROCESS OF PROTECTING A METAL SURFACE AGAINST CORROSION WHICHCOMPRISES APPLYING TO SAID SURFACE A SOLUTION COMPRISING A MAJORPROPORTION OF A LIQUID HYDROCARBON AND A MINOR PROPORTION OF OCTADECYLSULFAMIDO ACETIC ACID SODIUM SALT.